This invention relates generally to a method for detecting a locked axle condition for a vehicle and more particularly to a method for detecting a locked axle condition for an AC locomotive which is propelled by AC traction motors.
Locomotives used for hauling applications are generally equipped with speed sensors coupled to individual traction motors or to the axles driven by the traction motors. The speed sensor data or speed sensor information is monitored and used to detect a locked axle condition. If a locked axle condition occurs on a given axle while the locomotive is moving, the respective rotational axle speed will decrease to zero, while the remaining axles will continue to rotate at the speed corresponding to the speed of the locomotive. This locked axle condition will cause the axle wheel to slide along the rail and could adversely affect the handling characteristics of the locomotive. Thus, the speed sensor can usually detect a locked axle condition whenever a substantial difference in speed exists in one axle relative to the remaining axles.
When a locked axle is detected the locomotive operator generally has to stop the locomotive and inspect the axle for any visual damage. If there is no visual damage to the axle, then the locomotive is moved slightly in order to ascertain if the axle is in fact locked or if the detection of the locked axle is a false detection caused by a failure in the speed sensor. Using the current method of detecting a locked axle, when a locked axle condition is detected due to a failure in the speed sensor, the locked axle speed sensor and/or speed detection system is disabled and the locomotive is operated at a lower speed limit until the locked axle speed sensor and/or speed detection system can be repaired.
Unfortunately, this method has a number of disadvantages. One disadvantage is that stopping locomotives, inspecting axles and operating at slower speeds involve burdensome delays and can be expensive. A second disadvantage of this method is that it allows a large amount of electric power to be lost when an axle becomes locked. This is because the traction motor is driven by power supplied to the traction motor by the locomotive. When an axle becomes locked power is still supplied by the locomotive to drive the traction motor and this power becomes lost in the semiconductor devices of the traction motor. A third disadvantage is that if any of the electronic components of the locked axle speed sensor and/or speed detection system fails then locked axle detection is not possible. If the sensors do not function correctly, then a locked axle condition may occur without being detected.
Therefore, there is a need for a low-cost method to reliably determine when a locked axle condition occurs in a vehicle wherein the losses in the power semiconductors are minimized and wherein the method does not rely solely on axle speed sensors for locked axle detection.
A method for detecting a locked axle condition in a vehicle having a traction motor comprising: obtaining a traction motor signal having at least one phase, wherein the traction motor signal is responsive to the operating condition of the traction motor, processing the traction motor signal so as to create an indication result, and examining the indication result so as to determine if a locked axle condition exists.